Conventionally, within a water tank for breeding aquarium fish such as goldfish, tropical fish, or marine fish, with regard to a filter for filtering uncleaned water within the water tank, in which clean water from the filter is returned to the interior of the water tank through a shower tube, a cleaning device that cleans the interior of the shower tube by sliding a cleaning brush provided within the shower tube is known (ref. Patent Document 1 below).    Patent Document 1: Japanese Patent Application Laid-open No. 2004-243257